The prior art includes a range of designs of a sofa that can be converted into a bed. One such design is shown in U.S. Pat. No. 2,740,131. In this patent, a mechanism, in an unfolded position, has three sections, therein called respectively a “back section”, an “intermediate section”, and a “forward seating section”, and each section includes an integrally formed mattress portion having a surface defining a face of the section. Collectively the three sections form the bed. When the mechanism is in a folded position, the back section becomes the back portion of the sofa, the forward seating section becomes the seat support portion of the sofa, and the intermediate section is stowed in a generally horizontal position, beneath the forward seating support portion, and faces the floor. The stowed configuration is shown in FIG. 2 of the '131 patent.
U.S. Pat. No. 8,011,034 discloses an improvement over the design of U.S. Pat. No. 2,740,131. In U.S. Pat. No. 8,011,034, there are provided, as part of the mechanism, a head panel, a middle panel, and a foot panel (therein called respectively a “backrest panel”, a “subseat panel”, and a “seat panel”) and each panel has an attached mattress section (therein termed a “cushion”). The same general geometry applies as in the U.S. Pat. No. 2,740,131, except that, as suggested by FIG. 4 of U.S. Pat. No. 8,011,034, the improved design typically requires, when the mechanism is in the folded position, the addition of a removable seat and back cushions. In at least some embodiments, the geometry of the mechanism is such that the sofa frame must be specially designed to accommodate the mechanism, and the seat cushion must similarly be specially designed to satisfactorily overlie the seat panel, leading to a very bulky sofa frame.